Binders or cements which require acidic conditions to harden are well known in the prior art. For example, a zinc phosphate hydrate cement is produced by combining a metal oxide zinc powder with an acid such as phosphoric acid. When these two components are intermixed, rapid setting occurs and a high quality zinc hydrate cement will be formed.
Other acid-setting binders exist in the art and many have found wide use in a variety of industries. Acid-setting binders are used as dental cements, molding compositions when combined with fillers and reinforcing materials and as grouts to solidify loose soil, gravel or other building material.
Although these prior art cements have found wide acceptance, they possess certain drawbacks in practical application. Conventional methods require mixing of the cement components prior to placement within a suitable mold. As a result, the intermixed components tend to "set" prior to completion of the molding process. This premature hardening of the cement often results in a flawed product or clogged and damaged equipment. In addition, the rapid setting characteristic of the cement requires that all the mixing equipment be fully and completely cleaned immediately after transfer of the cement to the mold.
If an acid-setting cement or binder is used to produce a hollow article, conventional casting techniques require a mold which can be tumbled, rotated or rocked to allow a layer of unreacted cement to be uniformly distributed within the mold's interior. Consequently, loading of the mixed cement components within such casting equipment requires great care in order to ensure that none of the cement will set prior to complete coating of the interior of the mold.
Yet another disadvantage of acid-setting binders and cements is the need to prepare in advance the strong acid for addition to the metal oxide powder. Handling and preparation of such acids can be hazardous and requires great care on the part of the user. Further, articles produced with conventional acid-setting binders or cements are restricted by the type and number of filler materials which can be employed. Time constraints in terms of mixing and the need to avoid premature setting often make the inclusion of fillers within a finished product impractical or will yield a product of inferior quality.
Even though acid-setting cements and binders have found wide acceptance within the construction and molding industries, the uncontrolled speed at which they set has restricted their expansion into other technologies. A need has therefor existed within the art for acid-setting cements or binders which can be controllably hardened and in so doing avoid the aforementioned problems.